The use of a cocktail of drugs on Michael Jackson as he struggled to fall asleep was a "recipe for disaster" and ultimately caused his death, a sleep therapy expert said.

Dr Nader Kamanger described Dr Conrad Murray's treatment as "unethical, disturbing and beyond comprehension" at the trial of the cardiologist accused of the involuntary manslaughter of the pop megastar in June 2009. Murray denies the charge.

Dr Kamanger, one of the experts who evaluated Murray's actions for the California Medical Board, expressed dismay about the drugs Murray gave the pop star, his failure to immediately call for help and his lack of monitoring and record-keeping.

Authorities say Murray gave Jackson a fatal dose of propofol, a powerful anaesthetic used in surgeries.

Dr Kamanger was the third expert for the prosecution to criticise Murray's conduct. He said his first mistake was using propofol to treat insomnia, calling it an unacceptable application of the drug. "To summarise, Mr Jackson was receiving very inappropriate therapy in a home setting, receiving very potent therapies without monitoring," Dr Kamanger told the Los Angeles court.

He said diazepam (Valium), lorazepam (Ativan) and midazolam (Versed) were given to the sleepless star during a 10-hour period throughout the night and morning. "This cocktail was a recipe for disaster," Dr Kamanger said.

On Wednesday, Murray's defence team announced it was dropping a claim that was the centrepiece of their case - that Jackson swallowed additional propofol when Murray was out of the room. Mr Flanagan did not bring up self-dosing.

Murray could face up to four years behind bars and the loss of his medical licence if convicted.